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Fallback accretion on to a newborn magnetar: long GRBs with giant X-ray flares

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posted on 2019-08-20, 14:25 authored by S. L. Gibson, G. A. Wynn, B. P. Gompertz, P. T. O'Brien
Flares in the X-ray afterglow of gamma-ray bursts (GRBs) share more characteristics with the prompt emission than the afterglow, such as pulse profile and contained fluence. As a result, they are believed to originate from late-time activity of the central engine and can be used to constrain the overall energy budget. In this paper, we collect a sample of 19 long GRBs observed by Swift-XRT that contain giant flares in their X-ray afterglows. We fit this sample with a version of the magnetar propeller model, modified to include fallback accretion. This model has already successfully reproduced extended emission in short GRBs. Our best-fittings provide a reasonable morphological match to the light curves. However, 16 out of 19 of the fits require efficiencies for the propeller mechanism that approach 100 percent⁠. The high-efficiency parameters are a direct result of the high energy contained in the flares and the extreme duration of the dipole component, which forces either slow spin periods or low-magnetic fields. We find that even with the inclusion of significant fallback accretion, in all but a few cases it is energetically challenging to produce prompt emission, afterglow, and giant flares within the constraints of the rotational energy budget of a magnetar.


SLG would like to acknowledge funding from the Weizmann Institute and the University of Leicester. BPG has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no 725246, TEDE, PI A. Levan). PTO would like to acknowledge funding from STFC. This research used the Advanced Leicester Information Computational Environment (ALICE) High Performance Computing Facility at the University of Leicester. The work makes use of data supplied by the UKSSDC at the University of Leicester and the Swift satellite. Swift, launched in November 2004, is a NASA mission in partnership with the Italian Space Agency and the UK Space Agency. Swift is managed by NASA Goddard. Penn State University controls science and flight operations from the Mission Operations Centre in University Park, Pennsylvania. Los Alamos National Laboratory provides gamma-ray imaging analysis.



Monthly Notices of the Royal Astronomical Society, 2018, 478 (4), pp. 4323-4335 (13)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





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